This seems a pretty well approach. Let me try to implement it and see if it works. Thanks for the suggestion.

Actually I have an array of coordinates of the route using MKRoute.polyline.getcoordinates() method. But the distance between the coordinates of the route are uneven. Can you suggest how can I get every coordinate after 50 metres instead, So that I can check the distance upto 50 metres of accuracy ? Or can you tell me how can one find the closest coordinate of the route from the given coordinate ?